[Docs] Remove preamble and appendix texts

These will go into the global documentation

docs/appendix/00_index.rst

-Appendices of AlekSIS-Core
-==========================
-
-.. toctree::
-   :glob:
-
-   *

docs/appendix/99_eupl.rst

-../../LICENCE.rst
\ No newline at end of file

docs/index.rst

@@ -10,12 +10,10 @@ Welcome to AlekSIS-Core's documentation!
    :maxdepth: 2
    :caption: Contents:
 
-   preamble/00_index
    user/00_index
    admin/00_index
    dev/00_index
    ref/00_index
-   appendix/00_index
 
 
 Indices and tables

docs/preamble/00_index.rst

-Introduction to AlekSIS and the AlekSIS core
-============================================
-
-.. toctree::
-   :glob:
-
-   *

docs/preamble/01_introduction.rst

-Introduction to AlekSIS
-=======================
-
-Welcome
--------
-
-Welcome to AlekSIS, the Free School Information System! This handbook is
-a comprehensive guide on how to install, administer, and use AlekSIS and
-all included official apps. Its target audience are system
-administrators seeking to install and maintain an AlekSIS installation,
-people supporting the use of AlekSIS in daily processes in educational
-organisations, and end users who work with the software on a daily
-basis.
-
-On School Information Systems
------------------------------
-
-School Information Systems, or for short, SIS, are software suites that
-help educational organisations with managing personal information about
-all members (e.g. students, teachers, parents and guardians) as well as
-organisational data like plans, pedagogic track records, and much more.
-
-Generally, the goal of using School Information Systems is to help
-members of the school or other educational organisation to organise
-their work in learning and teaching, and to simplify digital processes,
-especially those that involve analytical evaluation, statistics, or
-information that is updated very frequently and should be made available
-to its recipients in a timely manner.
-
-Ideally, School Information Systems also promote transparency between
-teachers and students and improve sustainability by minimising the need
-for paperwork.
-
-AlekSIS, the Free School Information System
--------------------------------------------
-
-School Information Systems have been on the rise ever since schools
-began digitising their management processes. Traditionally, the vendors
-of school management tools (like for timetabling, personal data
-management of teachers and students, etc.) also deliver wen applications
-that are tailored towards making the respective data available to those
-who need it.
-
-As most of these solutions are proprietary products, they tend to be
-limited to be used together with other software of their vendors, and do
-not integrate nicely with other software and with processes and data
-sets not in the focus of the developers.
-
-AlekSIS, in contrast, is a generic School Information System that aims
-at being universally usable for all processes and data sets in any
-educational organisation, and at interacting closely with other software
-components employed in management and lessons. You can find information
-on the possibilities for interacting with other software in the chapter
-[@sec:Integrations].
-
-The development and product team has set the following goals for
-AlekSIS, in their dedication to support learning and teaching in the
-digital world:
-
--  Create a high-quality software product, adhering to high standards
-   regarding data protection, data safety, security, and stability
--  Comply with as many national and regional data protection and school
-   laws as possible (cf. [@sec:Legal])
--  Provide an extensible framework, allowing schools or their supporting
-   IT companies to create their own apps (cf. [@sec:Development])
--  Help coding clubs and classes to understand the development as deeply
-   as necessary to use AlekSIS for learning and creating their own apps
--  Keep AlekSIS free, open, and transparent (cf. [@sec:FOSS])